ANATOMY, PHYSIOLOGY, ETC. 
Ech. 7 
wise in juxtaposition, but separate from the ring of the aquiferous 
system. There is no organic connection between the “ rete mirabile '■ 
of the intestinal vascular system and the internal gills. The chief histo- 
logical elements of the nerves are longitudinal and transversal fibres and 
peripherical cells, the latter, perhaps, connected with the longitudinal 
nerve-fibres. Greeff (7, § 4, 2) has studied the “ Cuvierian organs,” 
occurring in some Holothuriidm (JT. poUiy e.g.), and agrees with Semper 
in regarding these elastic and glutinous filiform organs as weapons, which 
are protruded from the cloaca for defensive purposes. 
Anatomy of Echinidce. Teuscher (20) has likewise investigated several 
portions of the anatomy of Echinus esculentus and Spatangus “ meridion- 
alis” In Echinus^ there is a ventral and a dorsal intestinal vessel, and, 
in the upper winding of the intestine, a mesenterical vessel, which 
anastomoses frequently with the dorsal ; the ventral vessel is probably 
continued in an anal ring, though that could not be made out. The 
ventral intestinal vessel (perhaps also the dorsal) further communicates 
with the vascular ring encircling the oesophagus immediately above the 
“ lantern ” ; it probably gives origin (thus establishing a communication 
bet ween the intestinal and nouro-dormal systems) to the five sanguini- 
ferous vessels running down the pharynx ; close to the mouth, they are 
placed in juxtaposition with the five nerve-trunks, branching off from 
the nerve-ring situated within the lower extremities of the pyramids ; 
thus the central rings of the nervous and sanguiniferous systems are, in 
the Echini, placed at a certain distance from each other, separated by the 
whole height of the “ lantern.” Immediately below the vascular ringj 
lies the central ring of the aquiferous system, giving off (1) the stone canal, 
(2) the Polian vesicles (apparently abortive organs without any definite 
function like the so-called “ heart ” of the dorsal intestinal vessel), and 
(3) the five ambulacral vessels, running first horizontally below the 
rectangular covering-pieces of the lantern, afterwards perpendicularly 
down the outside of this organ, along the muscles between the pyramids, 
and finally turning upwards, in company with the five nerve-trunks and 
the five neuro-dermal vessels, on the inside of the shell. The ambulacral 
vessel is the innermost of the three, the nerve -trunk is enclosed in the 
neuro-dermal vessel, which gives off, like the nerve, a branch accom- 
panying each lateral branch of the water-tube to the ampullae and 
suckers. Between the intestine and the ventral vessel, is interposed, in 
a portion of the superior winding of the intestine, tlie “ organ of Hoff- 
man,” previously discovered in the Spatangi, an (abortive ?) diverticle of 
the intestine, communicating with its cavity at both extremities. A 
communication between the sanguiniferous and aquiferous systems was 
not made out in Echinus ; in Spatangus, a double communication of this 
kind exists : between the “ stone canal ” and the intestinal sanguiniferous 
system, and between this and the central ring of the ambulacral system. 
The central portion of the sanguiniferous system is, in Spatangus, a large 
oral sinus, enclosing in its interior the nerve-ring ; close to it, but out- 
side of the “ sinus,” the central ring of the aquiferous system is placed. 
L. Frederiq (5, 6) has also studied the nervous system in Echinus escu- 
lentus ; his description agrees in most points with that of Teuscher, but 
